2010 Cereal diseases and implications for 2011

| Date: 09 Feb 2011

Grant Hollaway, Mark McLean and Frank Henry

2010 in review
A widespread green bridge allowed the carry over of rust into the 2010 season. This carry- over of inoculum, combined with good rainfall, resulted in the widespread occurrence of stripe, leaf and stem rust in wheat where susceptible cultivars were grown. The importance of the green bridge in the carry over of rust was shown by the presence of stem and leaf rust on volunteer plants during the winter. In many cases, reductions to grain yield and quality occurred where these diseases were not managed.
The early start to the 2010 growing season favoured the development of stubble borne diseases such as yellow leaf spot in wheat, and scald and the spot form of net blotch in barley. Infection was especially severe when susceptible cultivars were sown into infected stubble. The cool, wet conditions during winter particularly favoured the development of scald in barley. This resulted in widespread and severe infections that required the application of fungicide sprays in many cases. Scald was also severe in some HindmarshA crops, indicating that this virulence is now common.
The spot form of net blotch of barley and yellow leaf spot of wheat were common in young plants, particularly in the Mallee. However, cool weather conditions restricted the progress of these diseases, and in most cases they did not become severe later in the season.
In general, root diseases were of low importance during 2010, but levels have increased and will be of potential concern for 2011. Look out for take-all, crown rot and rhizoctonia in 2011.
Stripe rust management experiment: 2010
The use of seed and foliar fungicides for the management of stripe rust in three wheat cultivars was compared in the field at Horsham during 2010. This research was done in collaboration with the University of Sydney. Because of the late appearance of rust (stripe rust did not become evident until after flag leaf emergence), seed applied fungicide or an early fungicide application (Z32) were of little benefit (Table 1). A single foliar fungicide application at flag leaf emergence (Z39) provided the best control of stripe rust.
Stripe rust severity differed between the wheat cultivars (Table 1). This demonstrates the importance of growing resistant cultivars, and avoiding the more susceptible cultivars for rust control. YitpiA, rated as MR-MS had the lowest level of stripe rust, followed by Janz (MS) and WyalkatchemA (MS-S).

Table 1. The effect of seed dressings and foliar fungicides on the severity of stripe rust in wheat (% flag leaf area affected on 20/10/10), Horsham 2010

TreatmentA
YitpiPBR logo
(MR-MS)
Janz
(MS)
WyalkatchemPBR logo
(MS-S)
Nil
13 aB
14 a
26 a
Jockey
10 ab
10 b
21 ab
Foliar @ Z32
4 bc
9 c
14 bc
Jockey + Foliar @ Z32
10 ab
8 c
4 cd
Foliar @ Z39
1 c
2 d
3 cd
Jockey + Foliar @ Z39
0 c
1 d
2 d
Foliar @ Z32 + Z39
2 c
1 d
2 d
Foliar @ 14 day intervals
2 c
1 d
1 d
P =
0.004
<0.001
<0.001
LSD =
7.0
1.9
11.5

AJockey® (167 g/L fluquinconazole) applied at 450 ml/100kg; Foliar fungicide Bumper® (250 g/L propiconazole) at 500 ml/ha at growth stages Z32 (stem elongation) and Z39 (flag leaf emergence).
BMeans within a column followed by the same letter are not significantly different (P=0.05).


Scald management trials: 2010
During 2010, two scald management experiments were undertaken. The first was in a commercial crop near Horsham, while the second was conducted in collaboration with the Birchip Cropping Group, at their Lubek trial site.
The first experiment was in a crop of GairdnerA naturally infected with scald. In early August, the crop was sprayed with a foliar fungicide Bumper® (250 g/L propiconazole) applied at 250 ml/ha at growth stage Z34 (4th node) and again at growth stage Z50 (ear emergence). This experiment showed that best control was achieved by the earlier of the two fungicide applications (Table 2). This indicates that scald was best controlled by applying a fungicide as early in the epidemic development as possible.

Table 2. Severity of scald (% flag leaf area affected on 20/10/10) after foliar applied fungicide in barley (cv. GairdnerA) at Quontong, near Horsham, 2010

TreatmentA
Scald Severity
Nil
20 aB
Z34
7 b
Z50
20 a
Z34 + Z50
6 b
P =
<0.001
LSD =
6.7

A Foliar fungicide Bumper® (250 g/L propiconazole) applied at 250 ml/ha at growth stage Z34 (4th node) and again at growth stage Z50 (ear emergence). BMeans followed by the same letter are not significantly different (P=0.05).

The second field experiment, at Lubeck, compared foliar, seed and fertiliser fungicides for scald management (Table 3). The foliar fungicide Bumper® (250 g/L propiconazole) applied at 250 ml/ha was most effective. Scald severity was decreased in response to multiple applications. The seed treatment Jockey® (167 g/L fluquinconazole) applied at 450 ml/100kg of seed was less effective, providing some reduction in scald severity, while the fertiliser treatment Impact In-furrow® (250 g/L flutriafol) applied at 400ml/100kg of fertiliser was not effective.


Table 3. Scald severity (% flag leaf area affected on 11/10/10) in cv. Yagan in response to seed, fertiliser and foliar fungicide treatments at Lubeck, 2010

Treatment
Scald severity
Nil
58 aB
Impact in furrow
55 a
Jockey
44 b
Foliar @ Z39 + Z55
4 c
Foliar @ Z25 + Z39 + Z55
0 c
P =
<0.001
LSD =
5.4

A Impact In-furrow® (250 g/L flutriafol) applied at 400ml/100kg of fertiliser. Jockey® (167 g/L fluquinconazole) applied at 450 ml/100kg of seed Foliar fungicide Bumper® (250 g/L propiconazole) applied at 250 ml/ha at growth stage Z25 (early tillering) Z39 (flag leaf emergence) and again at growth stage Z55 (half ear emergence). BMeans followed by the same letter are not significantly different (P=0.05).

Wheat: 2011
The risk of diseases in wheat will be high going into the 2011 season. There will be significant carry over of stubble borne diseases on the heavy loads of stubble and rust diseases on volunteer plants (green bridge) growing over summer. Avoiding susceptible and very susceptible cultivars, combined with the implementation of appropriate management strategies will be critical to minimise the impacts of disease during 2011.

Rust management
The significant summer rains across eastern Australia has resulted in an opportunity for the carry over of rust inoculum on volunteer crops (the green bridge) not seen since the 1970s. It is critical that the industry as a whole has a unified effort to manage volunteer cereals by the middle of March 2011 to reduce this threat.
Equally, it will be essential that cultivation of cultivars rated as very susceptible (VS), susceptible (S) and in some cases moderately susceptible (MS) be minimised. Due to the increased threat posed by the carry over of rust inoculum on the green bridge growers must have a plan to use fungicides to control rust in cultivars rated as MR-MS or lower. The use of seed or fertiliser applied fungicides at sowing followed up with foliar fungicides will be important during 2011.
During 2010, a new pathotype of stripe rust, that combines virulence for the resistance genes Yr17 and Yr27, was recorded in multiple locations in NSW. This new strain is important for the cultivar Livingstone which has both the Yr17 and Yr27 resistance genes, and also for the cultivars GBA RubyA and MerindaA which both have the Yr27 resistance. No new pathotypes of leaf or stem rust were detected, so only minor changes to ratings for these two diseases have occurred. Because of changes in rust pathogens it is important to always use a current cereal disease guide prepared for your region.
Yellow leaf spot inoculum levels will be high going into the 2011 season because of widespread occurrence of this disease during 2010. Avoid sowing susceptible wheat cultivars into paddocks where infected wheat stubble is present. Foliar fungicides are available to suppress yellow leaf spot development, but their effectiveness can be variable.

Septoria tritici blotch
This disease has been of minor importance during recent dry years. However, during 2010 there were several reports in the Victorian Western District. Septoria is more likely to be a problem in early sown susceptible crops that are exposed to frequent rainfall which disperses rain splashed spores.
Because of the increased inoculum levels during 2010, any wheat crops sown early in the higher rainfall regions of Victoria will be at heightened risk to infection by Septoria tritici blotch. Therefore, growers in the Western District of Victoria should have a plan to manage this disease by avoiding susceptible cultivars, avoiding early sowing and using seed and/or foliar applied fungicides to suppress this disease where needed.

White grain
In the lead up to the 2010 harvest, some Mallee wheat crops were found to be infected with the fungal disease white grain (caused by Botryosphaeria zeae). Infected grain was either downgraded to feed or rejected. There is little known about this disease, but infected grain is still suitable for stock feed. It has only been observed in seasons with significant rain late in the season. In the absence of another wet finish to the season it is unlikely to be an issue.

Barley: 2011

Scald
Scald was the most severe disease of barley during 2010. Its development was favoured by early sown crops and the cool, wet conditions during the winter months. It is likely that scald will be an important disease of early sown barley crops during 2011.
To minimise grain yield and quality loss from scald in 2011, avoid early sowing (April to mid May), and use seed and/or foliar applied fungicides to suppress disease development. It is important that crops are monitored for signs of scald to enable the application of a foliar fungicide early in the disease development.
Note that a strain of scald able to attack the cultivar HindmarshA has become common and therefore active management may be necessary when growing this cultivar.

Spot form of net blotch
Spot form of net blotch was widespread within Victorian barley crops during 2010, however, the cool weather conditions did not favour development, resulting in minimal loss. Inoculum levels for spot form of net blotch will be high going into the 2011 growing season and will, therefore require active management. To minimise the development of this disease, avoid susceptible and very susceptible cultivars and avoid sowing into paddocks with infected barley stubble. Foliar fungicides can be used to suppress the development of spot form of net blotch and are best applied between Z31 (stem elongation) and Z39 (flag leaf emergence).

Leaf rust and powdery mildew
Both these diseases will be favoured by carry over on the green bridge. These diseases can be managed by using seed applied fungicides, avoiding the more susceptible cultivars and monitoring with a view to timely foliar fungicide applications if warranted.

Oat: 2011
A number of diseases of oat were observed during 2010. These included stem and leaf rust, red leather leaf, bacterial blight and barley yellow dwarf virus. However, the biggest problem in oats was the failure to fill spikelets. This disorder was widespread, and as no one disease was found to be the cause of the problem, it likely it was caused by a physiological condition like frost.
It is expected that the high inoculum loads of stem and leaf rust will be carried into 2011 on the green bridge. Therefore, it will be important that foliar fungicides are used early to control rusts, especially in cultivars that have low levels of stem rust resistance. Fungicides have not been shown to be effective against red leather leaf.

Cereal Root Diseases: 2011
In general, root diseases were of little concern during 2010 due to low inoculum levels at the start of the season and favourable conditions. However, the wet spring will have increased the levels of take-all, crown rot and nematodes. Therefore, it will be important to consider root diseases this season, especially when planning to sow cereals into last year’s cereal paddocks. A pre-sowing soil test (PreDictaB) can be used to identify pre-sowing root disease levels and assist with implementation of management strategies as necessary.

More Information
More information is available on the DPI web site: www.dpi.vic.gov.au/notes
Contact details of author including
Grant Hollaway
Department of Primary Industries, Private Bag 260, Horsham, Victoria, 3401
email grant.hollaway@dpi.vic.gov.au

Mark McLean
Department of Primary Industries, Private Bag 260, Horsham, Victoria, 3401
email mark.mclean@dpi.vic.gov.au

Frank Henry
Department of Primary Industries, Private Bag 260, Horsham, Victoria, 3401
email frank.henry@dpi.vic.gov.au